Selena Gomez: I Was "Very Malnourished"

The pop star was hospitalized over the weekend

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Selena Gomez had to reschedule a concert because she was feeling nauseous and had a bad headache. She went to the hospital for routine tests.

Fans of Selena Gomez can rest easy-- the singer is out of the hospital and singing again.

The former star of Disney's "Wizards of Waverly Place" said she had to cancel her Friday Santa Monica concert because "I was just very malnourished, so I was low on iron and exhausted," People reported.

Selena Gomez On The End Of "Wizards Of Waverly Place": I Was "So Emotional"

After performing at KIIS FM"s 2011 Wango Tango Concert, Selena Gomez chats about the "emotional" last day of filming for her Disney series, "Wizards of Waverly Place." Also, Selena talks about her upcoming tour. (Published Tuesday, March 4, 2014)

But the 18-year-old was back on stage and ready to rock on Monday, greeting over 500 young fans at an outdoor mall.

"I want to thank you so much for coming," she said. "If you guys came on Friday, I'm so sorry that I couldn't be there... I love you guys very much."

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Looking as chipper as ever, Gomez belted out "Who Says" and "A Year Without Rain" without any problem, reassuring her fans, "I do feel better!"

Justin Bieber's girlfriend was feeling nauseous and had a huge headache after an appearance on NBC's Tonight Show with Jay Leno on Thursday. She was sent to a Los Angeles-area hospital for routine tests.